Patent Document 1 states that physical deposition under a vacuum environment is generally used as a method for forming a thin film of an organic material used in an organic electroluminescence device. Organic materials often decompose when kept for a long time at a vaporization temperature which is desirable for deposition or at a temperature closed to such a vaporization temperature. In particular, it has been pointed out that, when a temperature-sensitive organic material is heated to a higher temperature, the particle structure thereof may change, and with such a change in particle structure, the nature of the material may also change.
In the common vacuum deposition method, an organic material is put in a deposition source called a crucible, the organic material is evaporated by heating to a high temperature in a vacuum environment, whereby a thin film of an organic material is formed on a substrate. Since all of the material in a crucible is constantly heated to a high temperature, degradation of the material is accelerated. In addition, since the material is evaporated under a vacuum environment, it is difficult to control the evaporation direction of the material. Accordingly, more efficient use of a material contributing to film formation has become an object to be attained. Under such circumstances, the flash deposition method has attracted attention as the deposition means.
Patent Document 2 discloses a method in which an organic thin film of an organic thin-film electroluminescence device is obtained by the flash deposition method.
The flash deposition method is a method in which materials are supplied to a heated deposition source to allow them to evaporate quickly, whereby a deposited thin film (organic thin film) of an organic compound is formed on the surface of a substrate.
In flash deposition, a material for an organic thin film which is kept in a material-accommodating container is dropped through a screw part to a heat-deposition part which has been heated to 300 to 600° C., thereby to allow the material to be evaporated all at once. By outputting the evaporated material, through a heating conduit, towards a substrate which has been installed in advance, a film of an organic material is formed on the substrate. Heating in flash deposition is free from the problem that a material is constantly heated, since heating is performed while dropping a material to a deposition source. In addition, since the moving direction in which a heat-evaporated material can be controlled, a larger part of the material can be formed into a film. For these reasons, flash deposition has come to attract attention.
Generally, an organic EL device is a device in which an emitting layer containing a light-emitting organic compound (hereinafter referred to as “luminescent material) is held between a pair of electrodes. Electrons are injected from one of the electrodes, and holes are injected from the other electrode, and the injected electrons and holes are recombined in the emitting layer to emit light. A common organic EL device has a configuration in which an anode, a hole-transporting layer, an emitting layer, an electron-transporting layer and a cathode are stacked in this order. An emitting layer, a hole-transporting layer and an electron-transporting layer are respectively formed by forming an organic material into a film with a thickness of several nanometers to several tens nanometers. As an emitting layer, a material obtained by mixing a small amount of a dopant material (fluorescent material, phosphorescent material) with a host material forming an exciton is normally used.
Patent Document 1 discloses a deposition apparatus and a deposition method which shortens the time for which a deposition material is exposed to a high temperature. In this apparatus, a manifold provided with an opening is installed. A vaporized organic material is introduced into the manifold, and then a deposition material is supplied to a substrate through the opening thereof, followed by deposition.
Patent Documents 2 and 3 each disclose a method for producing an organic thin film of an organic thin film electroluminescence device using the flash deposition method. Patent Document 2 discloses a method in which a mixed material obtained by sufficiently mixing by means of an agate mortor or the like is supplied to a heated deposition source, followed by quick evaporation, thereby forming an organic thin film on the surface of a substrate. In this method, however, uniformity of the mixed material may be deteriorated before dropping to the deposition source. In this case, the ratio of each material which is dropped from a feeder changes with time, and as result, it is impossible to ensure uniformity of the ratios of the materials contained in an organic thin film formed by deposition.    Patent Document 1: JP-T-2008-519904    Patent Document 2: US-A-2007/0248753    Patent Document 3: JP-A-2008-530733
In view of the above-mentioned problem, an object of the invention is to provide a composite organic EL material suited to flash deposition, as well as to provide a method for producing the same.
The invention provides the following composite organic EL material or the like.    1. A composite organic electroluminescence material in which an organic material and an organic metal complex are combined with each other, wherein the melting point of the organic material is lower by 30° C. or more than the decomposition temperature of the organic metal complex.    2. The composite organic electroluminescence material according to 1, wherein the decomposition temperature is the temperature at which the weight of the organic metal complex is decreased by 1% when the organic metal complex is heated from room temperature at a heating rate of 10° C. per minute.    3. The composite organic electroluminescence material according to 1 or 2, wherein the molecular weight of the organic material is 2000 or less.    4. The composite organic electroluminescence material according to any one of 1 to 3, wherein the organic material is not an organic metal complex.    5. The composite organic electroluminescence material according to any one of 1 to 3, wherein
the organic material is a fused polycyclic aromatic compound of which the triplet energy value is in the range of 2.0 eV to 3.3 eV, and
the organic metal complex is an organic metal complex having a metal element selected from Ir, Pt, Os, Cu, Ru and Re as a central metal.    6. The composite organic electroluminescence material according to 5, wherein the fused polycyclic aromatic compound is a fused polycyclic aromatic hydrocarbon compound.    7. The composite organic electroluminescence material according to 5, wherein the fused polycyclic aromatic compound is a compound containing a heterocyclic ring.    8. The composite organic electroluminescence material according to any one of 1 to 7, wherein
the organic material is a host material contained in an emitting layer of an organic electroluminescence device, and
the organic metal complex is a phosphorescent dopant material contained in an emitting layer of an organic electroluminescence device.    9. A method for producing a composite organic electroluminescence material comprising:
mixing an organic material and a powdery organic metal complex to form a mixed material,
the melting point of the organic material measured by heating at a rate of 10° C. per minute being lower by 30° C. or more than the temperature at which the weight of the organic metal complex is decreased by 1% when the organic metal complex is heated from room temperature at a rate of 10° C. per minute;
heating the mixed material to a temperature which is lower by 30° C. or more than the temperature at which the weight of the organic metal complex is decreased by 1% when the organic metal complex is heated from room temperature at a rate of 10° C. per minute; and
cooling the heated mixed material.    10. The method for producing a composite organic electroluminescence material according to 9, which further comprising pulverizing the mixed material after the cooling.    11. A deposition method, comprising using the composite organic electroluminescence material according to any one of 1 to 8.
According to the invention, a composite organic EL material suited to flash deposition as well as a method for producing the same can be provided.
In addition, according to the invention, decomposition of raw materials during production of a composite material can be suppressed